Looks like slugs at work.

Uh oh...any thoughts on a good control method that's also natural?

I don't use any oils or pesticides for insect control as I grow organically. google Arbico. they specialize in beneficial insects. I ordered three praying manti egg cases. one for my yard and for my neighbors on both sides. one egg case hatches abou two hundred manti. They devour every insect you hate. and once they live out their life cycle they lay their own egg cases. so now I have an ongoing population of manti. I live an hour north of death Valley so its a desrt hot blazing summers freezing winters if my manti can stay alive year after year your area will support them as well. also consider Ladybugs these are literalyy the toughest bug in the pack they eat every single pest bug you can imagine problem is when they eat everything they move on to find more food. I even take my baby manti indoors to work over my bonsai and houseplants I leave a couple of windows open all the time for my cats to get in and out. so manti have an escape, or entrance if they choose. I grow vegetables, tobacco, fruit, housplants and bonsai. this was a permanent and inexpensive solution to my bug problem. Good Luck!!!!

Thanks for the detailed help, Sean! I've been hearing great things about ladybugs, but one post I found said it's a bad idea to purchase ladybugs en masse because they're usually stressed, from various regions, and of multiple strains, some of which are not native to the gardener's particular area and can cause problems. Just not sure. Love the praying manti suggestion--am calling my beneficial bug people to discuss.

Thanks again!
Gen

I remove mantises from my gardens because they go after more beneficial insects than pests. They'll lay in wait in my big Echinacea or zinnia for butterflies, for example. I've seen them snatch bees out of blossoms. They're not interested in aphids or slow moving caterpillars.

Gen, you need to find out if your problem is slugs, as as been suggested. Visit the garden in the evening, with a flashlight and prowl around. You might uncover slugs, earwigs, snails, caterpillars, etc....all of which would be more likely to be discovered at night.

Thanks, rhizo--I also found research about cabbage worm damage, which may be likely considering I did see lots of little white moth-y/butterfly things visiting my cabbage patch earlier in the Spring. I've harvested the bok choy since they started bolting in the heat, but I've still got to go prowling to solve this problem for the cabbages and cauliflower.

Thanks again!
Gen

Yep, those white moth-y/butterfly things just might be an important clue. ;-)